If x=1/4-y, evaluate
1/x + 4x + y -yx -1
please use parentheses!
i suppose you mean this:
If $\displaystyle x = \frac 1{4 - y}$, evaluate $\displaystyle \frac 1x + 4x + y - yx - 1$
note that, since $\displaystyle x = \frac 1{4 - y}$, we have $\displaystyle \frac 1x = 4 - y$
so our expression is:
$\displaystyle 4 - y + \frac 4{4 - y} + y - \frac y{4 - y} - 1$
now simplify